A plurality of settings are possible in digital x-ray imaging systems. On the one hand these are mechanical settings which are typically carried out prior to an image being recorded. Components which are adjusted mechanically include in particular the radiographic x-ray tube, the digital x-ray detector and usually also the patient examination table on which lies the patient of whom an x-ray image is to be taken. The mechanical settings can also include the setting of a filter if the latter is adjusted by hand by e.g. an operator.
Other settings relate to at least one control variable for the actual x-ray image. An example of a control variable of said kind is the voltage at the voltage generator, which voltage is used for the radiographic x-ray tube. Another control variable, typically specified with the aid of electrical signals, is the exposure time. The filter setting can also be included as a control variable, e.g. if it is electrically controlled and in particular is not associated in any way with mechanically movable components. A control variable can also be a value by means of which the recording system is specified, a distinction being made e.g. between automatic exposure system and two-point technique. The recording system indirectly specifies exposure time and possibly filter setting.
Once the settings have been performed mechanically on the respective components and also those of the control variables, means for capturing digital image information in the digital x-ray imaging system serve to record the actual digital x-ray image, which initially is unprocessed. The digital x-ray image can be stored, where necessary after a processing step, as part of an image dataset in a memory of the digital x-ray imaging system.
Frequently, digital x-ray images, once recorded, are used repeatedly, in particular when the treating physician wishes to observe the course of a medical condition. Typically, the physician will record, or arrange to have recorded, new digital x-ray images each time at various stages of the medical condition. In order to be able to recognize the course of the medical condition particularly well on the basis of the digital x-ray images it is important and advantageous if the later images are recorded using the same settings as the earlier images. In the prior art the persons recording the images attempt to deduce the settings for the image recording situation with the aid of the existing image, and then to reproduce said settings. This is difficult in particular in such cases in which the imaging is not performed fully automatically, but in which the user has to exert an influence over the mechanical settings from the outset, e.g. by hand. For example, certain x-ray images require an oblique irradiation from the tube onto the detector. Positioning, rotating and tilting the x-ray tube are then included among the tasks performed by the user. The lens aperture must also be set by the user. Even if the user subsequently still knows the settings for the voltage generator, he/she receives no help with regard to the alignment of the radiographic x-ray tube and the aperture setting when he/she wishes to restore the image recording situation of an earlier image.